1. Field of the Invention
This invention relates to sulfidoamidocarboxylic acids, a method for the production thereof, and uses therefor. More particularly, it relates to sulfidoamidocarboxylic acids, a method for the production thereof, and a corrosion inhibitor for metals, a composition comprising a sulfidoamidocarboxylic acid and a polyamine, a salt formed by the reaction of a sulfidoamidocarboxylic acid with a polyamine, and a corrosion inhibitor for metals containing the composition and/or the salt.
2. Description of the Related Art
When water is used as a working medium, the water exerts various effects on the metal. One of the effects is corrosion of metals. The corrosion of metals is an important problem in the maintenance and management of various facilities and devices that handle aqueous media. For this problem, corrosion inhibitors for metals are generally used.
The corrosion inhibitors for metals are known in numerous kinds including inorganic inhibitors such as chromates and phosphates and organic inhibitors such as alkyl amines and alkyl ammoniums. They are useful under specific conditions.
By situation of application, corrosion inhibitors for metals are used in two modes, i.e., closed system and open system. The use in the open system is particularly important because it directly relates to the environmental conservation. There are some cases when the chromates may possibly prove problematic in safety and the phosphates in eutrophication of the aqueous environment. Most alkyl amines and alkyl ammoniums manifest relatively high toxicity. From the viewpoint of protecting the environment, it is important to develop corrosion inhibitors for metals that enjoys high safety because of low toxicity, exerts only a small load on the environment, and proves highly effective.
I have found that low molecular weight sulfidoamines such as dimethylthiazolidine have an effect of corrosion inhibition for metals. When these amines do not call for gasifiability, there is a limit to use because of strong odor.
Except for the problem of the toxicity, the organic corrosion inhibitors, which are liable to decompose relatively easily in the natural environment, are attractive. The alkyl amines and the alkyl ammoniums exhibit toxicity. A cause for the toxicity is considered to have the nature of cationic soap, since this inference is supported by that the fatty acids (salts) having hydrocarbon groups of an equal size generally exhibit low toxicity. Since the fatty acids (salts) are surfactants, they generally do not seem to be used by themselves as a corrosion inhibitor for metals though are utilized as a component for corrosion inhibitors for metals.
Most fatty acids (salts) generally exhibit low toxicity as compared with the corresponding amines and ammoniums. An effort to improve their effects on corrosion inhibition and heightening the manifestation speed of such effects, constitute themselves important tasks for the development of corrosion inhibitors for metals expected to be low toxicity. Since the task of heightening the effect of corrosion inhibition automatically entails a decrease in the amount of an inhibitor to be used, it has an important significance in decreasing the load to be exerted on the environment.
When such a fatty acid (salt) is modified in molecular structure and consequently enabled to increase the effect of corrosion inhibition for metals, it is thought to provide a corrosion inhibitor for metals of low toxicity. Further, this fatty acid can be expected to exhibit high biodegradability when a partial structure liable to be decomposed with an enzyme is incorporated into the molecular structure.
On the basis of this theory, I have taken notice of carboxylic acids (salts) with an amide bond (amide bonds) in the molecular structures thereof. Such carboxylic acids with the amide bond can be expected to subject to hydrolysis caused by the amidases of microorganisms.
I have performed a study on sulfidoamidocarboxylic acids (salts) and have consequently found that the sulfidoamidocarboxylic acids (salts), i.e. the derivatives of dimethylthiazolidine, manifest an excellent effect of corrosion inhibition for metals. Moreover, these sulfidoamidocarboxylic acids (salts) emit only weak odor as compared with low molecular weight sulfidoamines such as dimethylthiazolidine (DMT) that generally entail the problem of emitting strong odor. It has been found by this study that sulfidoamidocarboxylic acids (salts) are useful as a corrosion inhibitor for metals. This invention has been perfected as a result.
It is an object of this invention to provide novel sulfidoamidocarboxylic acids (salts), a method for the production thereof, and uses therefor.
This invention concerns sulfidoamidocarboxylic acids (salts) represented by the formula I: 
wherein CnHm and Cnxe2x80x2Hmxe2x80x2 denote independently a hydrocarbon chain, CiHj denotes a hydrocarbon chain, n stands for an integer of 1-12, m for an integer of 2 to 2n, nxe2x80x2 for an integer of 1-15, mxe2x80x2 for an integer of 2 to 2nxe2x80x2, i for an integer of 2-20, j for an integer of 0 to 2i+2xe2x88x92kxe2x88x92z, k for an integer of 1-5, and z for an integer of 1-5, and M represents a hydrogen atom or a metal atom or an ammonium, i.e. an ammonium originating in NH3 or amines.
This invention also concerns a method for the production of sulfidoamidocarboxylic acids (salts) represented by the formula: 
wherein CnHm and Cnxe2x80x2Hmxe2x80x2 denote independently a hydrocarbon chain, CiHj denotes a hydrocarbon chain, n stands for an integer of 1-12, m for an integer of 2 to 2n, nxe2x80x2 for an integer of to 1-15, mxe2x80x2 for an integer of 2 to 2nxe2x80x2, i for an integer of 2-20, j for an integer of 0 to 2i+2xe2x88x92kxe2x88x92z, k for an integer of 1-5, and z for an integer of 1-5, and M represents a hydrogen atom or a metal atom or an ammonium, i.e. an ammonium originating in NH3 or amines, characterized by causing a sulfidoamine to react with an acid anhydride.
Further, this invention relates to a corrosion inhibitor for metals containing a sulfidoamidocarboxylic acid (salt) mentioned above.
In the following description, the group of compounds represented by the formula (I) will be referred to as xe2x80x9csulfidoamidocarboxylic acids (salts).xe2x80x9d
Though the sulfidoamidocarboxylic acid (salt) indeed manifests a high effect on corrosion inhibition for metals even at a low concentration, the speed of manifestion of the corrosion inhibition does not necessary deserve such a designation as xe2x80x9cvery highxe2x80x9d. On use in the circumstance, it is desirable to increase the speed at manifestion of corrosion inhibition without decreasing the maximal level of corrosion inhibition observed in the sulfidocarboxylic acid (salt). I have made a diligent study in search of a method for using sulfidocarboxylic acid (salt).
Polyethyleneimine effectively functions as a corrosion inhibitor in a bath for acid washing metal materials (JP-A-10-140379), and I have made a study on this action thereof in detail. As a result, I have found that this compound, when used at a low concentration in a neutral or weakly acidic aqueous medium, promotes the effect of sulfidoamidocarboxylic acids (salts) on corrosion inhibition for metals. The result means polyethyleneimine functioned as synergy for corrsion inhibition for metals.
I have made a diligent study in search of a method for using sulfidoamidocarboxylic acid (salt). This invention has been perfected as a result. A theory has prevailed that when the polyamine and the sulfidoamidocarboxylic acid (salt) independently functioned, their coexistance brings an effect that is the sum of their respective characteristic properties. From their respective characteristic properties, it has been impossible to infer the effect that forms the essence of this invention, i.e. the fact that their coexistence greatly increases the speed of manifestation of corrosion inhibition for metals.
This invention provides a novel composition for inhibiting corrosion of metals. The present invention concerns the following compositions.
[1] A composition containing polyamine (salt) and a sulfidoamidocarboxylic acid (salt) represented by the formula (I): 
wherein CnHm and Cnxe2x80x2Hmxe2x80x2 denote independently a hydrocarbon chain, CiHj denotes a hydrocarbon chain, n stands for an integer of 1-12, m for an integer of 2 to 2n, nxe2x80x2 for an integer of 1-15, mxe2x80x2 for an integer of 2 to 2nxe2x80x2, i for an integer of 2-20, j for an integer of 0 to 2i+2xe2x88x92kxe2x88x92z, k for an integer of 1-5, and z for an integer of 1-5, and M represents a hydrogen atom or a metal atom or an ammonium, i.e. an ammonium originating in NH3 or amines.
[2] A salt obtained from the reaction of a polyamine (salt) with a sulfidoamidocarboxylic acid (salt) represented by the formula: 
wherein CnHm and Cnxe2x80x2Hmxe2x80x2 denote independently a hydrocarbon chain, CiHj denotes a hydrocarbon chain, n stands for an integer of 1-12, m for an integer of 2 to 2n, nxe2x80x2 for an integer of 1-15, mxe2x80x2 for an integer of 2 to 2nxe2x80x2, i for an integer of 2-20, j for an integer of 0 to 2i+2xe2x88x92kxe2x88x92z, k for an integer of 1-5, and z for an integer of 1-5, and M represents a hydrogen atom or a metal atom or an ammonium, i.e. an ammonium originating in NH3 or amines.
[3] A composition for a corrosion inhibitor for metals containing a composition recited in [1] above and/or a salt incited in [2] above.
As a modification to [1] through [3] shown herein, a method for the corrosion inhibition which is characterized by causing polyethyleneimine (salt) and a sulfidoamidocarboxylic acid (salt) to be simultaneous presence, i.e. causing the two compound to mix or react with each other at the site of application, may be conceivable.
According to this invention, a sulfidoamidocarboxylic acid or a salt thereof can be provided.
Further, according to this invention, a method for producing a sulfidoamidocarboxylic acid (salt) by causing sulfidoamine to react with an acid anhydride can be provided.
Corrosion of metals can be inhibited with a sulfidoamidocarboxylic acid (salt) with a thiazolidine residue such as dimethylthiazolidine residue, a methylthiazolidine residue, or thiazolidine residue.
The sulfidoamidocarboxylic acid is enabled, by the addition thereto of polyamine, to expedite the manifestation of speed of corrosion inhibition of metals.
The above and other objects, features and advantages of the present invention will become clear from the following description of the preferred embodiments.
Corrosion inhibitors for metals hereafter may be referred as corrosion inhibitors.
The sulfidoamidocarboxylic acids (salts) to be used in this invention are generally represented by the formula I: 
In the formula I, CnHm and Cnxe2x80x2Hmxe2x80x2 independently signify a hydrocarbon chain and CiHj signifies a hydrocarbon chain. The sulfidoamidocarboxylic acids generally manifest their effect at a low concentration. In consideration of the solubility in water, it is highly proper to set the number of carbon atoms, n, at an integer of 1-12, the number of carbon atoms, nxe2x80x2, at an integer of 1-15, and the number of carbon atoms, i, at an integer of 2-20. As the number of hydrogen atoms, m is an integer of 2 to 2n, mxe2x80x2 an integer of 2 to 2nxe2x80x2, and j an integer of 2 to 2i+2xe2x88x92kxe2x88x92z and they respectively correspond to the numbers, n, nxe2x80x2, and i, of carbon atoms. While k is generally an integer of 1-5 and z an integer of 1-5, k=1 and z=1, k=2 and z=1, and k=2 and z=2, for example, are preferred choices of combinations. Particularly, k=1 and z=1 are frequently used. M signifies a hydrogen atom or a metal atom or ammonium, i.e. ammonium originating in NH3 or amines. In the case of a sulfidoamidocarboxylate, the ammonium originating in polyethyleneimine is also embraced in the scope of M. In the case of a free sulfidoamidocarboxylic acid, M denotes hydrogen atom.
Examples of sulfidoamidocarboxylic acids represented by the formula I may include DMT-amic acids originating in dimethylthiazolidine such as DMT-succinamic acid (amic acid formed by the reaction of succinic anhydride with DMT (dimethyl thiazolidine)), DMT-maleamic acid (amic acid formed by the reaction of maleic anhydride with DMT), DMT-phthalamic acid (amic acid formed by the reaction of phthalic anhydride with DMT), DMT-trimellitamic acid (amic acid formed by the reaction of trimellitic anhydride with DMT), DMT-pyromellitamic acid (amic acid formed by the reaction of pyromellitic dianhydride with DMT), DMT-mellitamic acid (amid acid formed by the reaction of mellitic trianhydride with DMT), DMT-hexahydrophthalamic acid (amic acid formed by the reaction of hexahydrophthalic anhydride with DMT), DMT-citraconamic acid (amic acid formed by the reaction of citrononic anhydride with DMT), DMT-itaconamic acid (amic acid formed by the reaction of itaconic anhydride with DMT), DMT-naphthalenedicarboxylamic acid (amic acid formed by the reaction of naphthalenedicarboxylic anhydride with DMT), amic acid formed by the reaction of maleated methyl cyclohexene tetracarboxylic dianhydride with DMT, DMT-endomethylenetetrahydrophthalamic acid (amic acid formed by the reaction of endomethylenetetrahydrophthalic anhydride with DMT), DMT-chlorendoamic acid (amic acid formed by the reaction of chlorendic anhydride with DMT), DMT-methylendomethylenetetrahydrophthalamic acid (amic acid formed by the reaction of methylendomethylenetetrahydrophthalic anhydride with DMT), DMT-methyltetrahydrophthalamic acid (amic acid formed by the reaction of methyltetrahydrophthalic anhydride with DMT), amic acid formed by the reaction of methylnorbornene-2,3-dicarboxylic anhydride with DMT, DMT-tetrahydrophthalamic acid (amic acid formed by the reaction of tetrahydrophthalic anhydride with DMT), amic acid formed by the reaction of cyclopentanetetracarboxylic anhydride with DMT, amic acid formed by the reaction of glutaric anhydride with DMT, DMT-dodecenylsuccinamic acid (amic acid formed by the reaction of dodecenylsuccinic anhydride with DMT), and DMT-hexahydromethylphthalamic acid (amic acid formed by the reaction of hexahydromethylphthalic anhydride with DMT);
MT-amic acids originating in methylthiazolidine such as MT-succinamic acid (amic acid formed by the reaction of succinic anhydride with MT (methylthiazolidine)), MT-maleamic acid (amic acid formed by the reaction of maleic anhydride with MT), MT-phthalamic acid (amic acid formed by the reaction of phthalic anhydride with MT), MT-trimellitamic acid (amic acid formed by the reaction of trimellitic anhydride with MT), MT-pyromellitamic acid (amic acid formed by the reaction of pyromellitic dianhydride with MT), MT-mellitamic acid (amic acid formed by the reaction of mellitic trianhydride with MT), MT-hexahydrophthalamic acid (amic acid formed by the reaction of hexahydrophthalic anhydride with MT), MT-citraconamic acid (amic acid formed by the reaction of citraconic anhydride with MT), MT-itaconamic acid (amic acid formed by the reaction of itaconic anhydride with MT), MT-naphthalenedicarboxylamic acid (amic acid formed by the reaction of naphthalenedicarboxylic anhydride with MT), amic acid formed by the reaction of maleated methylcyclohexanetetracarboxylic dianhydride with MT, MT-endomethylenetetrahydrophthalamic acid (amic acid formed by the reaction of endomethylenetetrahydrophthalic anhydride with MT), MT-chlorendamic acid (amic acid formed by the reaction of chlorendic anhydride with MT), MT-methylendomethylenetetrahydrophthalamic acid (amic acid formed by the reaction of methylendomethylenetetrahydrophthalic anhydride with MT), MT-methyltetrahydrophthalamic acid (amic acid formed by the reaction of methylendomethylenetetrahydrophthalic anhydride with MT), MT-methyltetrahydrophthalamic acid (amic acid formed by the reaction of methyltetrahydrophthalic anhydride with MT), amic acid formed by the reaction of methylnorbornene-2,3-dicarboxylic anhydride with MT, MT-tetrahydrophthalamic acid (amic acid formed by the reaction of tetrahydrophthalic anhydride with MT), amic acid formed by the reaction of cyclopentanetetracarboxylic dianhydride with MT, amic acid formed by the reaction of glutaric anhydride with MT, MT-dodecenylsuccinamic acid (amic acid formed by the reaction of dodecenylsuccinic anhydride with MT), and MT-hexahydromethylphthalamic acid (amic acid formed by the reaction of hexahydromethylphthalic anhydride with MT); and
T-amic acids originating in thiazolidine such as T-succinamic acid (amic acid formed by the reaction of succinic anhydride with T (thiazolidine)), T-maleamic acid (amic acid formed by the reaction of maleic anhydride with T), T-phthalamic acid (amic acid formed by the reaction of phthalic anhydride with T), T-trimellitamic acid (amic acid formed by the reaction of trimellitic anhydride with T), T-pyromelltamic acid (amic acid formed by the reaction of pyromellitic dianhydride with T), T-mellitamic acid (amic acid formed by the reaction of mellitic trianhydride with T), T-hexahydrophthalamic acid (amic acid formed by the reaction of hexahydrophthalic anhydride with T), T-citraconamic acid (amic acid formed by the reaction of citraconic anhydride with T), T-itaconamic acid (amic acid formed by the reaction of itaconic anhydride with T), T-naphthalenedicarboxylamic acid (amic acid formed by the reaction of naphthalenedicarboxylic anhydride with T), amic acid formed by the reaction of maleated methylcyclohexenetetracarboxylic dianhydride with T, T-endomethylenetetrahydrophthalamic acid (amic acid formed by the reaction of endomethylenetetrahydrophthalic anhydride with T), T-chlorendamic acid (amic acid formed by the reaction of chlorendic anhydride with T), T-methylendomethylenetetrahydrophthalamic acid (amic acid formed by the reaction of methylendomethylenetetrahydrophthalic anhydride with T), T-methyltetrahydrophthalamic acid (amic acid formed by the reaction of methyltetrahydrophthalic anhydride with T), amic acid formed by the reaction of methylnorbornene-2,3-dicarboxylic anhydride with T, T-tetrahydrophthalamic acid (amic acid formed by the reaction of tetrahydrophthalic anhydride with T), amic acid formed by the reaction of cyclopentanetetracarbocylic dianhydride with T, amic acid formed by the reaction of glutaric anhydride with T, T-dodecenylsuccinamic acid (amic acid formed by the reaction of dodecenylsuccinic anhydride with T), and T-hexahydromethylphthalamic acid (amic acid formed by the reaction of hexahydromethylphthalic anhydride with T).
Among other sulfidoamidocarboxylic acids enumerated above, DMT-succinamic acid, DMT-maleamic acid, DMT-phthalamic acid, DMT-trimellitamic acid, DMT-hexahydrophthalamic acid, and DMT-dodecenylsuccinamic acid are particularly preferred.
The sulfidoamidocarboxylic acids (salts) contemplated by this invention correspond to the compounds which result from partially amidating aliphatic or aromatic carboxylic acids possessing not less than two carboxyl groups in the molecular unit thereof (referred to in this invention as xe2x80x9cpolycarboxylic acidsxe2x80x9d) with sulfidoamine. The sulfidoamidocarboxylic acids (salts) of this invention, therefore, are synthesized by a method which comprises subjecting a polycarboxylic acid and sulfidoamine to dehydrating condensation or causing a sulfidoamine to react with a chloride or an ester or anhydride of a polycarboxylic acid, for example.
In these methods, the method which comprising causing sulfidoamine to react with the intramolecular anhydride (with within the molecular unit a cyclic structure allowing the presence of xe2x80x94COxe2x80x94Oxe2x80x94COxe2x80x94) of polycarboxylic acid proves particularly preferable. The reason for this preference is that the reaction is not only allowed to proceed without readily generation of by-products but also enabled, by controlling the reaction temperature, to proceed in the absence of solvents.
The acid anhydrides, which serve as raw materials for synthesis of sulfidoamidocarboxylic acids (salts), may include the following compounds: Succinic anhydride, maleic anhydride, phthalic anhydride, trimellitic anhydride, pyromellitic dianhydride, mellitic anhydride, cyclohexanedicarboxylic anhydride, citraconic anhydride, itaconic anhydride, naphthalenedicarboxylic anhydride, maleated methylcyclohexanetetracarboxylic dianhydride, endomethylenetetrahydrophthalic anhydride (norbornene-endo-2,3-dicarboxylic anhydride), chlorendic anhydride, methylendomethylenetetrahydrophthalic anhydride, methyltetrahydrophthalic anhydride, methylnorbornene-2,3-dicarboxylic anhydride, tetrahydrophthalic anhydride, cyclopentanetetracarboxylic dianhydride, glutaric anhydride, dodecenylsuccinic anhydride, and hexahydromethylphthalic anhydride.
Among other acid anhydrides enumerated above, phthalic anhydride, trimellitic anhydride, pyromellitic dianhydride, naphthalenedicarboxylic anhydride, cyclohexanedicarboxylic anhydride, succinic anhydride, maleic anhydride, and dodecenylsuccinic anhydride prove favorable and succinic anhydride, maleic anhydride, phthalic anhydride, and trimellitic anhydride prove particularly favorable in respect that they allow easy production of acid anhydrides. By causing these anhydrides to react with a sulfidoamine, sulfidoamidocarboxylic acids, such as succinamic acid, maleamic acid, phthalamic acid, and trimellitamic acid are synthesized easily.
If the number of carbon atoms of an acid anhydride to be used is unduly large, the excess generally will entail the disadvantage in that the solubility of the consequently formed sulfidoamidocarboxylic acid (salt) decreases. In consideration of the water solubility of the sulfidoamidocarboxylic acid or the dispersibility thereof in water, it is inferred that the number of carbon atoms in the polycarboxylic acid residue has the upper limit thereof in the proximity of 22. Though the lower limit of the number of carbon atoms ought to be theoretically allowed to fall as far down as 2, it is appropriately not less than 4 in consideration of the feasibility of the synthesis. The sulfidoamidocarboxylic acid (salt) with cyclohexanedicarboxylic acid residue has a greater ability to inhibit corrosion than that of the sulfidoamidocarboxylic acid (salt) with succinic acid residue. This result implies that the number of carbon atoms is preferred to be greater than a certain degree. Thus, for this invention, the number of carbon atoms i in the formula (I) is preferred to be not less than 5. The proper number of carbon atoms shown here pertains mainly to saturated aliphatic polycarboxylic acid residues and embraces such favorable exceptions as maleic acid residues, which are unsaturated polycarboxylic acid residues.
For the corrosion inhibitors containing a compound represented by the formula I, it is appropriate that i stands for an integer of 2-20, preferably an integer 3-14, j for an integer of 0 to 2i+2xe2x88x92kxe2x88x92z, k for an integer of 1-5, z for an integer of 1-5, and M for a hydrogen atom, a metal atom, or ammonium as mentioned above. Examples of the metal atom mentioned above may include alkali metal atom and alkaline earth metal atom. Among other metal atom mentioned above, alkali metal atom proves favorable and lithium, sodium, and potassium prove particularly favorable. When a divalent or trivalent metal atom is used as a metal atom M, half of the atom of divalent metal, Mgxc2xd, Caxc2xd, Srxc2xd, Baxc2xd, Znxc2xd, Cuxc2xd, Fexc2xd for example, or one-third of the atom of trivalent metal, Al⅓, Fe⅓, La⅓, Ce⅓ for example, is equivalent to M.
The hydrocarbon chains, xe2x80x94CnHmxe2x80x94 and xe2x80x94Cnxe2x80x2Hmxe2x80x2xe2x80x94, which are in the sulfidoamidocarboxylic acids (salts) of this invention, are generally aliphatic hydrocarbon chains with a linear or branched chain structure. The hydrocarbon chains with an aromatic ring or an aromatic cyclic structure are also usable, depending on the purpose for which the relevant acids are used. If the hydrocarbon chains, xe2x80x94CnHmxe2x80x94 and xe2x80x94Cnxe2x80x2Hmxe2x80x2xe2x80x94, are unduly large, they will be at a disadvantage that the water solubility of the sulfidoamidocarboxylic acids (salts) or the dispersibility thereof in water decreases. In consideration of the stability of sulfidoamidocarboxylic acids (salts), it is advantageous for the hydrocarbon chains, xe2x80x94CnHmxe2x80x94 and xe2x80x94Cnxe2x80x2Hmxe2x80x2xe2x80x94, that n denotes an integer of 1-12, m an integer of 2 to 2n, nxe2x80x2 an integer of 1-15, and mxe2x80x2 an integer of 2 to 2nxe2x80x2.
As concrete examples of the sulfidoamidocarboxylic acids (salts) of this invention, thiazolidine residues such as dimethylthiazolidine, methylthiazolidine, and thiazolidine residues and polycarboxylic acid (salt) residues such as dicarboxylic acid (salt), tricarboxylic acid (salt), and tetracarboxylic acid (salt) residues have already been cited.
As the raw materials for the synthesis of such sulfidoamidocarboxylic acids, thiazolidines are advantageously used.
The thiazolidines and the thiazolidine residues have a five-membered cyclic structure including a nitrogen atom and a sulfur atom. In this case, the minimum numbers of n and nxe2x80x2 are 2 and 1 respectively. Also in this case, the condition that n is an integer of 1-12, m an integer of 2 to 2n, nxe2x80x2 an integer of 1-15, and mxe2x80x2 an integer of 2 to 2nxe2x80x2 is satisfied. In the 2,2-dimethylthiazolidine, which is used particularly preferably in this invention, CnHm is C2H4 and Cnxe2x80x2Hmxe2x80x2 is C3H6.
The compounds analogous to thiazolidines may be designated by using xe2x80x94CRRxe2x80x2xe2x80x94 instead of xe2x80x94Cnxe2x80x2Hmxe2x80x2xe2x80x94 (as shown in the formula II). In this case, the groups R and Rxe2x80x2 independently denote a hydrogen atom or a hydrocarbon group. Their sizes are preferred to be equivalent approximately to not more than 12 carbon atoms. More preferably, the total carbon atoms in these two groups are not more than 12. 
As particularly preferred sulfidoamine residues, dimethylthiazolidine residues (hereinafter abbreviated as R, Rxe2x80x2xe2x95x90CH3, DMTxe2x80x94), methylthiazolidine residues (hereinafter abbreviated as Rxe2x95x90CH3, Rxe2x80x2xe2x95x90H, MTxe2x80x94), and thiazolidine residues (hereinafter abbreviated as R, Rxe2x80x2xe2x95x90H, Txe2x80x94) may be cited.
As other sulfidoamine residues, thiomorpholine residues, thiomorpholines residues with structures originating respectively in thiomorpholine and thiomorpholines are hopeful.
The number of the sulfidoamine residues is decided in accordance with the acid anhydride to be used for the synthesis. In consideration of performance in use or industrial utilizability, the number is preferred to be in the range of 1-5. In the sulfidoamidocarboxylic acids (salts), z is preferred in the range of 1-5.
The amounts of an acid anhydride and a sulfidoamine to be used in their reaction are generally such that the equivalent ratio of the partial structure, xe2x80x94COxe2x80x94Oxe2x80x94COxe2x80x94, in the acid anhydride to the sulfidoamine is generally in the range of 1-3:3-1, preferably in the range of 1-1.5: 1.5-1, and especially 1:1. The term xe2x80x9cequivalent ratio 1:1xe2x80x9d as used herein designates 1:1 (molar ratio) in the case of the reaction of a monoanhydride such as succinic anhydride, maleic anhydride, phthalic anhydride, or trimellitic anhydride with thiazolidine, methylthiazolidine, or dimethylthiazolidine, 1:2 (molar ratio) where the acid anhydride is a dianhydride such as pyrollitic dianhydride, or 1:3 (molar ratio) where the acid anhydride is a trianhydride such as mellitic trianhydride.
In this invention, it is advantageous to use succinic anhydride, maleic anhydride, phthalic anhydride, or trimellitic anhydride as the acid anhydride and dimethylthiazolidine (available from Nippon Shokubai Co., Ltd.) as the sulfidoamine. When they are used for the reaction, it is particularly advantageous to use them at an equivalent ratio of 1:1 because this equivalent ratio allows warrants smooth progress of the relevant reaction. When the reaction between the acid anhydride and sulfidoamine (the reaction for forming an amide bond) proceeds smoothly, the product can be handled as a sulfidoamidocarboxylic acid without being further purified. As the corrosion inhibitor, i.e. the use contemplated by this invention, the product can be used as it is or after purification if necessary.
The reaction temperature between the acid anhydride and sulfidoamine is not particularly restricted but only required to be capable of inducing a reaction of the acid anhydride with sulfidoamine. It is generally in the range of below ice cooling (0xc2x0 C.)-120xc2x0 C., preferably in the range of 15-120xc2x0 C.
The reaction duration between the acid anhydride and sulfidoamine, which terminates when the generation of the reaction heat ceases to be observed, is generally not less than two minutes, and preferably in the approximate range of 2-60 minutes. Prolonged reaction time may be needed depending on reaction temperature.
The reaction between the acid anhydride and sulfidoamine is carried out in the absence of a solvent or in the presence of a solvent. Examples of the solvent to be used for the reaction may include various organic solvents of ketones such as acetone and methyl ethyl ketone; ethers such as diethyl ether and dimethoxyethane; halogenated solvents such as dichloromethane and carbon tetrachloride; and hydrocarbons such as hexane, petroleum ether, ligroin, benzene, toluene, and xylene. Though the amount of such a solvent to be used is not particularly limited, it is properly 0-10 times, preferably 0-2 times (not inclusive of 0) the total amount of the raw materials used.
The reaction can be carried out generally in the atmosphere of an inert gas such as nitrogen or argon. When such a solvent as acetone is used in an amount of not less than 1 time the amount of the raw materials, the reaction can be carried out under the atmosphere of air because the vapor of the solvent is enabled to cover the surface of the reaction product at the temperature of heating under ambient atmospheric pressure. Even when small amount of solvent less than 1 time the amount of the raw material or no solvent is used, the reaction may be carried out under the atmosphere of air, depending on the conditions of the operation involved. Though the reaction pressure is not particularly limited, it may be ambient atmospheric pressure.
The sulfidoamidocarboxylic acid, which is formed by the reaction between an acid anhydride and a sulfidoamine, may be neutralized into a salt with an inorganic base or an organic base depending on the purpose of use. Here, the term xe2x80x9cinorganic basexe2x80x9d embraces substances similar to the inorganic base, and the term xe2x80x9corganic basexe2x80x9d embraces substances similar to the organic base. Examples of the inorganic bases and the substances similar to the inorganic bases may include lithium hydroxide, sodium hydroxide, potassium hydroxide, lithium carbonate, sodium carbonate, potassium carbonate, lithium hydrogen carbonate, sodium hydrogen carbonate, potassium hydrogen carbonate, ammonia, ammonium carbonate, and ammonium hydrogen carbonate. Depending on the condition under which the corrosion inhibitor is used, oxides, hydroxides, carbonates, or hydrogen carbonates of magnesium, calcium, and strontium, for example, may be also used as inorganic base. Examples of the organic bases and the substances similar to the organic bases may include alkylamines, dialkylamines, and trialkylamines such as ethanolamine, diethanolamine, triethanolamine, allylamine, diallylamine, methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, and triethylamine. As organic bases, dimethylthiazolidine, methylthiazolidine, thiazolidine, cysteamine, and polyamines which will be described more specifically herein below may be also used, depending on the purpose of use. The term xe2x80x9cammoniumsxe2x80x9d as used herein means amines such as have a hydrogen ion bonded thereto and ammonium (NH4).
First of all, raw substances to be used in this invention will be described.
In this invention, various species of polyamine can be used. The term xe2x80x9cpolyaminexe2x80x9d as used herein means xe2x80x9can organic compound including not less than two amino groups,xe2x80x9d preferably xe2x80x9can organic compound including not less than 10 amino groups on the average in the molecular unit thereof.xe2x80x9d The term xe2x80x9camino groupxe2x80x9d as used herein means xe2x80x94NH2, xe2x80x94NHxe2x80x94, N (call for three monovalent coupling bonds) that have not formed an amide structure bond. As one example of the amino group, polyethyleneimine may be cited. The polyethyleneimine is a polyamine type polymer including (xe2x80x94CH2xe2x80x94CH2xe2x80x94NHxe2x80x94) as the monomer unit. Examples of the macromolecule including a nitrogen atom in the side-chain portion may include polyvinylamine (xe2x80x94CH2xe2x80x94CH(NH2)xe2x80x94 as the monomer unit), polyallylamine (xe2x80x94CH2xe2x80x94CH(CH2NH2)xe2x80x94 as the monomer unit), etc. Besides, diamines such as H2Nxe2x80x94(CH2CH2O)xxe2x80x94NH2 (x=13 where the molecular weight is about 600) and H2Nxe2x80x94(CH2CH(CH3)O)xxe2x80x94NH2 (x=10 where the molecular weight is about 600) may be cited.
In the examples of this invention, polyethyleneimine (having a number average molecular weight of 70000, available from Nippon Shokubai Co., Ltd.) was preferentially used as the polyamine. As inferred from the function of polyethyleneimine, which will be discussed hereinafter, the use of polyvinylamine or polyallylamine can be expected to bring the same function or effect as the polyethyleneimine.
No particular restriction is originally imposed on the lower limit or the upper limit of the molecular weight of polyamine. When this molecular weight decreases to approximate closely to that of ethylenediamine or diethylenetriamine, it is considered that the polyamine will bring about the problem of toxicity. Thus, the molecular weight at which the polyamine is supposed to be difficult in passing a cell membrane, serves as the criterion for the lower limit of the molecular weight. It is generally held that in the case of a low molecular compound, the compound will cease easily passing a cell membrane when the molecular weight exceeds about 600. It is, therefore, allowed to set the lower limit of the molecular weight of polyamine at 600 as the standard. No restriction is originally imposed on the upper limit of the molecular weight so long as the compound has solubility in water and solubility in an organic solvent. As concrete examples of the commercially available polyamine, polyethyleneimine preferentially used in Examples 8-10 has a molecular weight in the neighborhood of 70,000 and polyallylamine a molecular weight in the approximate range of 10,000-100,000. In consideration of the proper range of molecular weight, it may be in the range of 0.0085-100 times, preferably 0.01-100 times, more preferably 0.1-10 times, the molecular weight of 70,000 as the center.
The salt of sulfidoamidocarboxylic acid with polyamine to be used in this invention is preferably obtained by the reaction of sulfidoamidocarboxylic acid with polyamine. This reaction is a simple neutralization reaction of a base and an acid which is induced by mixing the base and the acid. The reaction can be effected in the absence of a solvent or in the presence of water, an aqueous solvent, or an organic solvent. The reaction temperature is not particularly restricted but only required to be in a range in which the polyamine and the sulfidoamidocarboxylic acid are not decomposed. The reaction temperature for practical use is in the approximate range of 0 to 100xc2x0 C., preferably in the approximate range of 0 to 50xc2x0 C., and especially in the approximate range of 10 to 40xc2x0 C. The ratio of the amounts of polyamine and sulfidoamidocarboxylic acid to be used for the reaction is 1:1 in equivalent ratio as the standard where the reaction forms a normal salt. It maybe in the range from 1:1 in equivalent ratio to 1:1 in molar ratio where the reaction forms a basic salt.
The polyamine is usually treated as a simple substance. It is not only an aggregate of macromolecules that differ in size as viewed on the molecular level, but also the reactivity of the existing amino groups is not uniform. In the synthesis of a salt of sulfidoamidocarboxylic acid with polyamine, it is one of the realistic choices to continue the reaction between the polyamine and the sulfidoamidocarboxylic acid by adding one of the reactants to the other, while sampling the reaction mixture, converting the sample into an aqueous solution, and then testing the aqueous solution for hydrogen ion concentration with a pH test paper or a pH meter. By this method, various salts or a mixture containing such salts manifesting acidity through basicity can be synthesized, and the degree of acidity or the degree of basicity can be selected depending on the purpose of use.
In consideration of the fact that in this invention a mixture of polyamine with a sulfidoamidocarboxylic acid can be used as a corrosion inhibitor for metals, the mixing ratio of the amounts of the polyamine and the sulfidoamidocarboxylic acid may be set in the range of 10:1 to 1:10, and even in the range of 300:1 to 1:000 in weight ratio. In this mixture, the salt is formed from a polyamine and a sulfidoamidocarboxylic acid.
In the formation of a salt of sulfidoamidocarboxylic acid with polyamine, it may be used a sulfidoamidocarboxylate instead of the sulfidoamidocarboxylic acid. Ammonium sulfidoamidocarboxylate, for example, is thought to react with the polyamine and liberate ammonia to form the salt of polyamine consequently. Alternatively, the salt may be formed by double decomposition. A metal salt of sulfidoamidocarboxylic acid such as sodium sulfidoamidocarboxylate, instead of a free acid, may be caused to react with a salt of polyamine instead of a polyamine, for example, a chloride salt or a sulfate salt.
The mixture of a polyamine with a sulfidoamidocarboxylic acid (salt) for use in this invention can be prepared by mixing these materials in the absence of solvents or in the presence of water, an aqueous solvent, or an organic solvent. Here, an aqueous solvent means a mixture of water and organic solvents such as aqueous methanol, aqueous ethanol, aqueous propanol, aqueous acetone, for example. Though the mixing ratio of these two materials is preferably selected in the range of 3:1 to 1:3 in weight ratio, it may be selected in the range of 10:1 to 1:10 and, depending on the conditions, may be selected in the range of 300:1 to 1:100.
The mixture of a salt of polyamine with a sulfidoamidocarboxylic acid can also be prepared in same manner.
The polyamine (salt) and the sulfidoamidocarboxylic acid (salt) can be easily mixed or caused to react with each other in water, an aqueous solvent or an organic solvent. For practical utilization of this invention, the method may be adopted which comprises simultaneously introducing the polyamine (salt) and the sulfidoamidocarboxylic acid (salt) to a given site of application, e.g., water, sea water and allowing them to coexist at the site, namely mixing them or allowing them to react with each other thereby inhibiting corrosion. The reason is that this method results in forming a composition and/or a salt of polyamine (salt) with the sulfidoamidocarboxylic acid (salt), though generally in the form of a dilute solution.
The corrosion inhibitor and the composition therefor contemplated by this invention are intended to inhibit corrosion by increasing the polarization resistance. They, therefore, can be applied not only to iron type metals such as iron and iron alloys, e.g., carbon steel and stainless steel but also to metals in general which can be expected to increase polarization resistance. Examples of the object for application may include copper and copper alloys such as brass and cupro-nickel, zinc and zinc alloys, magnesium and magnesium alloys, aluminum and aluminum alloys, nickel and nickel alloys, chromium and chromium alloys, and lead, tin, manganese, cobalt, molybdenum, tungsten, vanadium, and cadmium and the alloys thereof besides the iron type metals mentioned above.
The compound of this invention is a compound represented by the structural formula (I) mentioned above and is useful as a corrosion inhibitor for metals, for example.
The compound represented by the formula, which is analogous to the compound represented by the formula (I), may be used as a corrosion inhibitor for metals:
(HSCnHmNHCO)zCiHj(COOM)k
wherein n, m, i, j, z, k, and M have the same meanings as in the formula (I).
Examples of the compound represented by the formula mentioned above may include N-(mercaptoethyl) succinamic acid, N-(mercaptoethyl)maleamic acid, N-(mercaptoethyl)phthalamic acid, N-(mercaptoethyl)trimellitamic acid (dicarboxylic acid,i.e., k=2), N-(mercaptoethyl)dodecenylsuccunamic acid, N-(mercaptopropyl)succinamic acid, N-(mercaptopropyl)maleamic acid, N-(mercaptopropyl)trimellitamic acid (dicarboxylic acid), N-(mercaptopropyl)dodecenylsuccinamic acid, N-(mercaptophenyl)succinamic acid, N-(mercaptophenyl)maleamic acid, N-(mercaptophenyl)phthalamic acid, N-(mercaptophenyl)trimellitamic acid (dicarboxylic acid), N-(mercaptophenyl)dodecenylsuccinamic acid. These compounds are also useful as corrosion inhibitors for metals.